The present invention relates to a vacuum brake booster for automotive vehicles and is of the type having a vacuum housing sealingly subdivided into a vacuum chamber and a working chamber by an axially movable wall which is prestressed by a return spring. A mechanically actuable control valve connects the working chamber to the vacuum chamber or the atmosphere. The axially movable housing of the control valve is made of thermoplastic material and accommodates, within an axial bore, a rubber-elastic reaction disk which is abutted by a push rod for transmitting the braking force to an actuating piston of a master cylinder which is mounted on the vacuum housing on the vacuum side. The movable wall is connected to the control valve housing and a guide sleeve, having a radial flange, serves to guide the push rod axially.
A vacuum brake booster of this type is disclosed in U.S. Pat. No. 4,892,027 entitled "Vacuum Brake Power Booster for Automotive Vehicles and Method for Its Manufacture" which corresponds to German Published Patent Application (DE-OS) No. 37 09 172. In the brake booster disclosed in U.S. Pat. No. 4,892,027, the radial flange of the guide sleeve is axially supported within the bore of the control valve housing which receives the reaction disk and is retained axially, in a positive manner, by a holding element connected to the control valve housing. The holding element is formed either by a radial shoulder on the control valve housing or by radially inwardly directed projections formed on the control valve housing or on a retaining ring, with the outside or inside surface of the retaining ring being attached to the surface of the control valve housing, for example, by ultrasonic or friction welding or by an adhesive. The arrangements just described can suffer from inaccuracies, might be unsafe, and can involve high cost.
In another vacuum brake booster disclosed in U.S. Pat. No. 4,898,073 entitled "Vacuum Brake Force Booster for Use with Automotive Vehicles" which corresponds to German Patent Application No. 37 40 691.4, the guide sleeve has an axial extension which is provided to eliminate the danger of damage to the control valve housing in the area of support for the guide sleeve. Both the reaction disk and an abutting pressure plate are received in the axial extension of the guide sleeve which, in turn, is fitted and sealed in the axial bore of the control valve housing. In the brake booster disclosed in U.S. Pat. No. 4,898,073, the radial support of the axial extension of the guide sleeve is provided only by the wall of the axial bore in the control valve housing in an area of small wall thickness, so that the control valve housing can be susceptible to damage due to bending forces acting on the push rod.